1. Technical Field
This invention relates generally to stripline microwave antenna feed systems and, more particularly, to a compact low-profile wideband microwave antenna mode forming network such as a Butler matrix.
2. Discussion
Microwave antenna feed systems are generally known for directly feeding the input: and/or output ports of a multiple-port antenna system so as to achieve multiple antenna beam and/or mode control. One class of microwave antenna feed systems are commonly known as Butler matrices. Currently, Butler matrices are used in conjunction with airborne microwave electronic warfare and communication systems for purposes of providing instantaneous direction finding and multi-beam jamming of microwave signals A conventional Butler matrix generally feeds (N) feed elements of a multi-port antenna system and provides the ability to operate with (M) radiating modes or beams. A typical Butler matrix generally includes a number of 90 or 180 degree hybrid couplers along with a number of fixed phase shifters which are usually electrically interconnected via phase-trimmed coaxial cables.
Currently, commercially available Butler matrices include the ninety degree (90.degree.) type manufactured by Anaren which is located in, Syracuse, N.Y. and having Model Nos. 182570 and 182580. These particular Butler matrices include eight (N=8) antenna ports and eight (M=8) receive/transmit ports and are capable of providing simultaneous multiple beam transmission and/or receiving bearing information. However, such commercially available Butler matrix mode forming networks generally involve a rather large, heavy and complex packaging arrangement, especially those networks which are capable of providing a large number of beams.
The complex packaging associated with prior networks typically includes a large number of electrical components arranged in a bulky layout and coupled to one another by way of cross-over transmission lines. Typical circuit layouts further require multilayer signal interconnections which may become unwieldy and cause the feeds to exhibit high insertion loss due to ohmic and mismatch loss. In addition, the commercially available Butler matrix networks are generally capable of operating effectively over a very limited frequency range. For instance, typical operating ranges include frequencies between 7-15 GHz or 12-18 GHz. Such limited frequency ranges are usually rather narrow and generally do not extend into higher frequencies such as those exceeding 20 GHz.
Current and future trends in airborne electronic warfare and communication technologies require that Butler matrices provide increasingly wider instantaneous bandwidths. For instance, there is an increasing need to achieve multioctave performance up to Ku band frequencies and above so as to allow for operation across, the entire microwave band. In addition, there is an increasing need to provide for a larger number of antenna modes or beams in a smaller more light weight package. Furthermore, it is desirable to decrease the costs associated with manufacturing Butler matrices such as the costs generally involved in attempting to meet stringent cable phase-trimming requirements.
It is therefore desirable to provide for an improved low-profile Butler matrix modeforming network which is capable of operating over wide instantaneous bandwidths. More particularly, it is desirable to provide for such a Butler matrix network which exhibits high frequency multioctave operating capabilities. In addition, it is desirable to provide for a Butler matrix modeforming network which is capable of providing a large number of antenna modes in a small lightweight package which exhibits rather low energy loss.